State of the art LED light bulbs and other electronics contain printed circuit boards (PCBs) and other electronic components which must be electrically isolated from user contact. These devices must also have sufficient thermal management to keep operating temperatures below a critical value to extend service life. A number of workers in this area have attempted to provide plastic, polymer materials to assist in the thermal management.
U.S. Pat. No. 7,235,918, issued to McCullough et al., provides a thermally-conductive polymer composition suitable for making molded reflector articles having light-reflecting surfaces. The composition contains: a) about 20% to about 80% by weight of a base polymer matrix, such as polycarbonate; and b) about 20% to about 80% by weight of a thermally-conductive carbon material, such as graphite. The composition is said to be useful in making reflector articles such as housings for automotive tail lamps, head lamps, and other lighting fixtures. A method for manufacturing reflector articles is also provided by McCullough et al.
Brown in U.S. Published Patent Application No. 2008/0287585 details thermally-conductive compositions and reaction tubes for chemical- and biochemical-based analytical processing. The compositions and reaction tubes contain at least one plastic and at least one compound having a higher thermal conductivity than the at least one plastic to result in compositions and tubes having increased thermal conductivity when compared to the at least one plastic alone. Such compositions and tubes are said to be capable of facilitating rapid heat transfer in numerous heat transfer applications. The thermally-conductive compositions and reaction tubes of Brown are said to be especially suitable for containing reaction constituents during thermal cycling of the polymerase chain reaction (PCR).
JP 2009-161582, in the name of Maruyama et al., provides a conductive polycarbonate resin composition said to have excellent antistaticity, electromagnetic wave-shielding property, mechanical strengths, thermal stability, and appearance. The polycarbonate resin composition contains (A) 50 to 90 wt. % of a polycarbonate resin and (B) 50 to 10 wt. % of graphite, wherein the concentration of silicon in the graphite (B) is ≤1,000 ppm.
Fujioka et al., in U.S. Published Patent Application No. 2010/0072416, describe a heat-dissipating resin composition that is said to be useful for forming a substrate for LED mounting or a reflector provided on the substrate for LED mounting and is excellent in heat dissipation, electrical insulation, heat resistance and light resistance while an LED element emits light, a substrate for LED mounting and a reflector comprising the composition. The composition of Fujioka et al. contains a thermoplastic resin such as modified polybutylene terephthalate and a thermally conductive filler consisting of scaly boron nitride or the like, and has thermal deformation temperature of 120° C. or higher, a thermal conductivity of 2.0 W/(mK) or higher, and a thermal emissivity of 0.7 or higher.
U.S. Published Patent Application No. 2011/0095690 in the name of Sagal discloses an LED lighting apparatus which includes an electronic circuit board having a peripheral portion and a central portion that is radially inward of said peripheral portion, said electronic circuit board having an exterior side for optically interfacing with ambient environment during operation and an interior side opposite the exterior side. At least one LED is mounted on the exterior side of the electronic circuit board central portion and a thermally conductive housing encloses said electronic circuit board, said thermally conductive housing formed of a moldable thermally conductive material. The thermally conductive housing defines a first cavity adjacent the central portion of the electronic circuit board exterior side and a second cavity adjacent the central portion of the electronic circuit board interior side, wherein a portion of said thermally conductive housing being overmolded onto said peripheral portion.
Janssen et al., in U.S. Published Patent Application No. 2011/0103021, describe a heatsink for an electrical or electronic device comprising a plastic body made of a thermally conductive plastic material comprising of an expanded graphite in an amount of at least 20 wt. %, relative to the total weight of the thermally conductive plastic material.
U.S. Published Patent Application No. 2011/0281051 in the name of Dufaure et al. discloses an expanded graphite, in which the specific surface is between 15 and 30 m2/g, the apparent density is less than 0.1 g/cm3, for an average particle size of more than 15 μm, to grant a thermoplastic polymer properties of thermal, electric and rheological conductivity suitable for the transformation of said polymer.
Takeuchi et al., in PCT Published Patent Application No. WO 2011/013645, describe a polycarbonate resin composition which contains, per 100 parts by mass of (A) a polycarbonate resin, 30-100 parts by mass of (B) artificial graphite, 0.01-5 parts by mass of (C) an organopolysiloxane that has a group selected from among a phenyl group, a methoxy group and a vinyl group, and 0.01-5 parts by mass of (D) a fluorine compound. Also disclosed are: a molded body which is obtained by molding the polycarbonate resin composition; and a component for an electrical/electronic device, a case for an electrical/electronic device and a chassis for an electrical/electronic device, each comprising the molded body. The polycarbonate resin composition provides a molded article which is said to have high thermal conductivity and high mechanical strength, while exhibiting high flame retardancy even in cases when the molded article is formed thin.
U.S. Pat. No. 8,221,885, issued to Miller, describes an injection moldable, thermally conductive polymer composition said to have ultra low CTE properties and suitable both for substrate applications in high precision electronics assemblies as well as over molding applications in conjunction with ceramic substrates. The composition includes a base polymer matrix material loaded with thermally conductive filler, which is said to impart thermal conductivity to the polymer matrix while also maintaining or enhancing the dielectric properties of the base polymer. Miller says the resultant composition exhibits CTE properties in the range of between 9 ppm/° C. and 2 ppm/° C., exhibits an optical anisotropy of below 1.5, and a thermal conductivity of greater than 2 W/m° K. The composition of Miller is said to be suitable for use in over molding applications in conjunction with virtually any suitable electronics substrate material without the introduction of mechanical stresses produced by large CTE differentials.
Li et al, in U.S. Published Patent Application No. 2012/0319031, describe a composition containing about 90% to about 30% of at least one amorphous thermoplastic or at least one semi crystalline thermoplastic or a mixture thereof and about 10% to about 70% of expanded graphite, wherein about 90% of the particles of the expanded graphite have a particle size of at least about 200 microns. The compositions of Li et al. are said to be useful use in LED heat sink applications.
The above cited references teach, in general, that thermally conductive fillers are added to thermoplastic resin to make the resultant composite thermally conductive. These thermally conductive fillers can be carbon based, such as carbon fibers, graphites, and carbon black. They can be ceramic-based, such as boron nitride, aluminum carbide.
A need continues to exist in the art for further improvements to materials for use in thermal management in electronic devices such as LED lamps.